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Date:   Fri, 28 Oct 2022 12:03:51 -0400
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Subject: Re: [PATCH 2/5] iommu/s390: Add I/O TLB ops
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To:     Niklas Schnelle <schnelle@linux.ibm.com>, iommu@lists.linux.dev,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jason Gunthorpe <jgg@nvidia.com>
Cc:     Gerd Bayer <gbayer@linux.ibm.com>,
        Pierre Morel <pmorel@linux.ibm.com>,
        linux-s390@vger.kernel.org, borntraeger@linux.ibm.com,
        hca@linux.ibm.com, gor@linux.ibm.com,
        gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com,
        svens@linux.ibm.com, linux-kernel@vger.kernel.org
References: <20221018145132.998866-1-schnelle@linux.ibm.com>
 <20221018145132.998866-3-schnelle@linux.ibm.com>
From:   Matthew Rosato <mjrosato@linux.ibm.com>
In-Reply-To: <20221018145132.998866-3-schnelle@linux.ibm.com>
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On 10/18/22 10:51 AM, Niklas Schnelle wrote:
> Currently s390-iommu does an I/O TLB flush (RPCIT) for every update of
> the I/O translation table explicitly. For one this is wasteful since
> RPCIT can be skipped after a mapping operation if zdev->tlb_refresh is
> unset. Moreover we can do a single RPCIT for a range of pages including
> whne doing lazy unmapping.
> 
> Thankfully both of these optimizations can be achieved by implementing
> the IOMMU operations common code provides for the different types of I/O
> tlb flushes:
> 
>  * flush_iotlb_all: Flushes the I/O TLB for the entire IOVA space
>  * iotlb_sync:  Flushes the I/O TLB for a range of pages that can be
>    gathered up, for example to implement lazy unmapping.
>  * iotlb_sync_map: Flushes the I/O TLB after a mapping operation
> 
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
>  drivers/iommu/s390-iommu.c | 76 ++++++++++++++++++++++++++++++++------
>  1 file changed, 65 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> index ee88e717254b..a4c2e9bc6d83 100644
> --- a/drivers/iommu/s390-iommu.c
> +++ b/drivers/iommu/s390-iommu.c
> @@ -199,14 +199,72 @@ static void s390_iommu_release_device(struct device *dev)
>  		__s390_iommu_detach_device(zdev);
>  }
>  
> +static void s390_iommu_flush_iotlb_all(struct iommu_domain *domain)
> +{
> +	struct s390_domain *s390_domain = to_s390_domain(domain);
> +	struct zpci_dev *zdev;
> +	unsigned long flags;
> +	int rc;
> +
> +	spin_lock_irqsave(&s390_domain->list_lock, flags);
> +	list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
> +		rc = zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma,
> +					zdev->end_dma - zdev->start_dma + 1);
> +		if (rc)
> +			break;
> +	}
> +	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> +}
> +
> +static void s390_iommu_iotlb_sync(struct iommu_domain *domain,
> +				  struct iommu_iotlb_gather *gather)
> +{
> +	struct s390_domain *s390_domain = to_s390_domain(domain);
> +	size_t size = gather->end - gather->start + 1;
> +	struct zpci_dev *zdev;
> +	unsigned long flags;
> +	int rc;
> +
> +	/* If gather was never added to there is nothing to flush */
> +	if (gather->start == ULONG_MAX)
> +		return;

Hmm, this seems a little awkward in that it depends on the init value in iommu_iotlb_gather_init never changing.  I don't see any other iommu drivers doing this -- Is there no other way to tell there's nothing to flush?

If we really need to do this, maybe some shared #define in iommu.h that is used in iommu_iotlb_gather_init and here?

> +
> +	spin_lock_irqsave(&s390_domain->list_lock, flags);
> +	list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
> +		rc = zpci_refresh_trans((u64)zdev->fh << 32, gather->start,
> +					size);
> +		if (rc)
> +			break;
> +	}
> +	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> +}
> +
> +static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain,
> +				      unsigned long iova, size_t size)
> +{
> +	struct s390_domain *s390_domain = to_s390_domain(domain);
> +	struct zpci_dev *zdev;
> +	unsigned long flags;
> +	int rc;
> +
> +	spin_lock_irqsave(&s390_domain->list_lock, flags);
> +	list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
> +		if (!zdev->tlb_refresh)
> +			continue;
> +		rc = zpci_refresh_trans((u64)zdev->fh << 32,
> +					iova, size);
> +		if (rc)
> +			break;
> +	}
> +	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> +}
> +
>  static int s390_iommu_update_trans(struct s390_domain *s390_domain,
>  				   phys_addr_t pa, dma_addr_t dma_addr,
>  				   unsigned long nr_pages, int flags)
>  {
>  	phys_addr_t page_addr = pa & PAGE_MASK;
> -	dma_addr_t start_dma_addr = dma_addr;
>  	unsigned long irq_flags, i;
> -	struct zpci_dev *zdev;
>  	unsigned long *entry;
>  	int rc = 0;
>  
> @@ -225,15 +283,6 @@ static int s390_iommu_update_trans(struct s390_domain *s390_domain,
>  		dma_addr += PAGE_SIZE;
>  	}
>  
> -	spin_lock(&s390_domain->list_lock);
> -	list_for_each_entry(zdev, &s390_domain->devices, iommu_list) {
> -		rc = zpci_refresh_trans((u64)zdev->fh << 32,
> -					start_dma_addr, nr_pages * PAGE_SIZE);
> -		if (rc)
> -			break;
> -	}
> -	spin_unlock(&s390_domain->list_lock);
> -
>  undo_cpu_trans:
>  	if (rc && ((flags & ZPCI_PTE_VALID_MASK) == ZPCI_PTE_VALID)) {
>  		flags = ZPCI_PTE_INVALID;
> @@ -340,6 +389,8 @@ static size_t s390_iommu_unmap_pages(struct iommu_domain *domain,
>  	if (rc)
>  		return 0;
>  
> +	iommu_iotlb_gather_add_range(gather, iova, size);
> +
>  	return size;
>  }
>  
> @@ -384,6 +435,9 @@ static const struct iommu_ops s390_iommu_ops = {
>  		.detach_dev	= s390_iommu_detach_device,
>  		.map_pages	= s390_iommu_map_pages,
>  		.unmap_pages	= s390_iommu_unmap_pages,
> +		.flush_iotlb_all = s390_iommu_flush_iotlb_all,
> +		.iotlb_sync      = s390_iommu_iotlb_sync,
> +		.iotlb_sync_map  = s390_iommu_iotlb_sync_map,
>  		.iova_to_phys	= s390_iommu_iova_to_phys,
>  		.free		= s390_domain_free,
>  	}